Olefins are important intermediates in the manufacture of many commodity petrochemicals. For instance, high octane gasoline is produced on a large scale by alkylation of isoparaffins, such as isobutane or isopentane, with olefins, such as propylene or butenes. In HF alkylation, the secondary butene isomer, 2-butene, gives a higher octane alkylate than 1-butene, and is therefore the preferred feed.
The four C.sub.4 mono-olefins, 1-butene, cis-2-butene, trans-2-butene and 2-methylpropene are collectively called butylenes. The term isobutylene is by established usage interchangeable with the nomenclature 2-methylpropene, while the other three isomers are n-butenes. Often they are treated collectively because the four mono-olefins are obtained as mixtures, from natural gas and from petroleum refinery processes. The C.sub.4 olefins are often contained in mixtures of C.sub.1 -C.sub.5 hydrocarbons, which include both alkanes and alkenes.
One object of the invention is to convert n-butene(s) to 2-butene. An object of the process is to produce 2-butene with high selectivity.
Another object of the process of this invention is to convert n-butenes to isobutylene. Isobutylene is a desirable reactant for the production of alkylate, which includes high octane gasoline components, and for the production of methyl-t-butyl ether, when isobutylene is reacted with methanol. A conventional process for separation of isobutylene from the other three components involves sulfuric acid extraction or selective adsorption, as the isomers cannot be separated by simple extraction. Acid extraction is cumbersome and includes as an undesirable aspect the oligomerization of the components themselves.